Oppositions to the petitions are due by Sept. 17. Replies to those pleadings have to be filed by Oct. 9.

Petitions to deny a merger are often submitted by advocacy groups and competitors, but they're open to the public.

T-Mobile and Sprint have long looked at a potential collaboration, given that rivals Verizon and AT&T are much bigger companies, and a merger would help level the playing field. T-Mobile and Sprint considered striking a deal in 2014, but regulators and the White House weren't on board. The Trump administration and the FCC have been more open to deals, and in April the companies finally announced they'd merge.